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Regioselectivity of Electrophilic Additions-Peroxide Effect

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In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.

Radical Anti-Markovnikov Addition to Alkenes: Overview

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The addition of hydrogen bromide to alkenes in the presence of hydroperoxides or peroxides proceeds via an anti-Markovnikov pathway and yields alkyl bromides.

Halogenation of Alkenes

Halogenation of Alkenes

Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.

Radical Substitution: Allylic Bromination

Radical Substitution: Allylic Bromination

In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...

Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism

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Birch reduction uses solvated electrons as reducing agents. The reaction converts benzene to 1,4-cyclohexadiene. The reaction proceeds by the transfer of a single electron to the ring to form a benzene radical anion. This anion is highly basic—it abstracts a proton from the alcohol to form a cyclohexadienyl radical. Another single electron transfer gives the cyclohexadienyl anion. A proton transfer from the alcohol forms 1,4-cyclohexadiene. Since this reduction occurs via radical anion...

Electrophilic Aromatic Substitution: Chlorination and Bromination of Benzene

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Chlorination and bromination are important classes of electrophilic aromatic substitutions, where benzene reacts with chlorine or bromine in the presence of a Lewis acid catalyst to give halogenated substitution products. A Lewis acid such as aluminium chloride or ferric chloride catalyzes the chlorination, and ferric bromide catalyzes the bromination reactions. During the bromination of alkenes, bromine polarizes and becomes electrophilic. However, in the bromination of benzene, the bromine...

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Related Experiment Video

Updated: Mar 10, 2026

A Facile Synthetic Method to Obtain Bismuth Oxyiodide Microspheres Highly Functional for the Photocatalytic Processes of Water Depuration

A Facile Synthetic Method to Obtain Bismuth Oxyiodide Microspheres Highly Functional for the Photocatalytic Processes of Water Depuration

Published on: March 29, 2019

Engineering the Electronic Microenvironment with Bromine Functionalization for High-Selectivity Photocatalytic CO₂

Junhui He^1,2, Zhansheng Wang², Jiang Xue¹

¹CAEA Innovation Center of Nuclear Environmental Safety Technology, School of Environment and Resource, School of National Defense & Nuclear Science and Technology, Southwest University of Science and Technology, Mianyang, Sichuan, P. R. China.

Small (Weinheim an Der Bergstrasse, Germany)

|March 9, 2026

Summary

This summary is machine-generated.

Surface bromine modification of covalent organic frameworks (COFs) enhances CO2 photoreduction. This strategy improves catalyst activity and selectivity for efficient carbon dioxide conversion.

Keywords:

Br functionalization TzPm‐COF‐2Br photocatalytic CO2 reduction

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Published on: July 25, 2025

Area of Science:

Materials Science
Photocatalysis
Green Chemistry

Background:

Covalent organic frameworks (COFs) are promising materials for photocatalysis.
Tuning the electronic structure of COFs is crucial for enhancing their performance.
Surface modification offers a route to optimize COF properties.

Purpose of the Study:

To investigate the effect of surface bromine atom modification on TzPm-COF.
To enhance the activity and selectivity of CO2 photoreduction using modified COFs.
To elucidate the mechanism behind the improved photocatalytic performance.

Main Methods:

Synthesis of bromine-modified TzPm-COF (TzPm-COF-2Br).
In situ Kelvin probe force microscopy (KPFM) and spectral analysis.
Density functional theory (DFT) calculations.

Main Results:

Bromine functionalization of TzPm-COF significantly enhanced CO2 photoreduction activity (155 µmol g⁻¹ h⁻¹).
The modified COF exhibited high selectivity (99.4%) for CO production.
Bromine atoms facilitated charge carrier separation and migration, improving CO2 adsorption and activation.

Conclusions:

Surface bromine modification is an effective strategy for tuning COF donor-acceptor structures.
The enhanced TzPm-COF-2Br shows superior performance for visible-light-driven CO2 reduction.
This work provides a rational design approach for developing advanced COF photocatalysts.